The available overlays are grouped into "background" (rasters, only one can be selected at a time)
and "foreground" (line features, any number can be selected).

Individual overlays are selected from the list offered, and can first be individually inspected.

For the new map to be generated, the user can select whether the results of the composer
should be temporary (only for inspection) or permanent (optional saving to the map catalog);
A square domain can be enforced, an origin (X/Y), and an extent. If the selection is to be permanent, a name for he new map can be specified.

An organge button "generate" will trigger the actual map generation.

Once the combination of overlays yields a satisfactory results, the new map
can be named and saved to the map catalog.